Ground Based Synoptic Instrumentation for Solar Observations
08 Sep 2011-Proceedings of SPIE (International Society for Optics and Photonics)-Vol. 8148, pp 814809
TL;DR: In this article, the status of current ground-based solar spectroscopic and imaging instruments is described and the advantages and disadvantages of using these two classes of instruments with examples drawn from the Improved Solar Optical Observing Network (ISOON) and Synoptic Long Term Investigations of the Sun (SOLIS) networks.
Abstract: We will describe the status of current ground-based solar spectroscopic and imaging instruments
used in solar observations. We will describe the advantages and disadvantages of using these
two classes of instruments with examples drawn from the Improved Solar Optical Observing
Network (ISOON) and Synoptic Long Term Investigations of the Sun (SOLIS) Network.
Besides instrumental requirements and lessons learned from existing ground-based instruments,
this talk will also focus on the future needs and requirements of ground-based solar optical
observations.
Citations
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TL;DR: In this article, the physical mechanisms responsible for solar eruptions were major unanswered questions in solar and by extension stellar physics, and new observations of CME dynamics and associated eruptive phenomena are now providing more stringent constraints on m...
Abstract: Solar eruptions, observed as flares and coronal mass ejections (CMEs), are the most energetic visible plasma phenomena in the solar system. CMEs are the central component of solar eruptions and are detected as coherent magnetized plasma structures expanding in the solar wind (SW). If they reach the Earth, their magnetic fields can drive strong disturbances in the ionosphere, causing deleterious effects on terrestrial technological systems. The scientific and practical importance of CMEs has led to numerous satellite missions observing the Sun and SW. This has culminated in the ability to continuously observe CMEs expanding from the Sun to 1 AU, where the magnetic fields and plasma parameters of the evolved structures (“ejecta”) can be measured in situ. Until recently, the physical mechanisms responsible for eruptions were major unanswered questions in solar and by extension stellar physics. New observations of CME dynamics and associated eruptive phenomena are now providing more stringent constraints on m...
71 citations
TL;DR: In this paper, the Carrington maps of the photospheric vector magnetic field were used to study the hemispheric pattern of current helicity density, Hc, during the rising phase of solar cycle 24.
Abstract: We use daily full-disk vector magnetograms from Vector Spectromagnetograph on Synoptic Optical Long-term Investigations of the Sun system to synthesize the first Carrington maps of the photospheric vector magnetic field. We describe these maps and make a comparison of the observed radial field with the radial field estimate from line-of-sight magnetograms. Furthermore, we employ these maps to study the hemispheric pattern of current helicity density, Hc , during the rising phase of solar cycle 24. The longitudinal average over the 23 consecutive solar rotations shows a clear signature of the hemispheric helicity rule, i.e., Hc is predominantly negative in the north and positive in the south. Although our data include the early phase of cycle 24, there appears to be no evidence for a possible (systematic) reversal of the hemispheric helicity rule at the beginning of the cycle as predicted by some dynamo models. Furthermore, we compute the hemispheric pattern in active region latitudes (–30° ≤ θ ≤ 30°) separately for weak (100 G 1000 G) radial magnetic fields. We find that while the current helicity of strong fields follows the well-known hemispheric rule (i.e., θ · Hc 0), albeit with large statistical scatter. We discuss two plausible scenarios to explain the opposite hemispheric trend of helicity in weak and strong field regions.
64 citations
TL;DR: In this paper, the authors developed a new proxy to represent the evolution of magnetic activity in past solar cycles by combining the information from historical Ca II K line spectroheliograms and sunspot magnetic field measurements.
Abstract: Aims. The present work is the first in a series of articles that develop a new proxy to represent the evolution of magnetic activity in past solar cycles by combining the information from historical Ca II K line spectroheliograms and sunspot magnetic field measurements.Methods. We use synoptic (Carrington) maps from 1915–1985 that were derived from daily Ca K line observations at Mount Wilson Observatory to identify the chromospheric plages and to create synoptic pseudo-magnetograms. We use historical observations of sunspot magnetic fields from 1917 to the present to assign polarity to pixels situated within plages. The original Ca K spectroheliograms are nonuniform in their brightness, and we develop a novel approach to re-normalize their intensities.Results. We show that a homogeneous long-term series of pseudo-magnetograms can be successfully constructed by combining sunspot field measurements and plages with renormalized intensities. In our tests, about 80% of pixels situated within plages showed the same magnetic polarity as the synoptic magnetograms taken with the Kitt Peak Vacuum Telescope. Finally, we discuss possible approaches to further improve the agreement between observed and pseudo-magnetograms.
60 citations
Cites methods from "Ground Based Synoptic Instrumentati..."
...Fortunately, data from the Vector Stokes Magnetograph (VSM) on the Synoptic Optical Long-term Investigation of the Sun (SOLIS) facility (Balasubramaniam & Pevtsov 2011) allow addressing this question....
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TL;DR: In this article, the amplitude and energy flux of compressive waves in the solar corona were explored using a spacecraft radio occultation technique using a frequency time series taken at heliocentric distances of 1.5-20.5
Abstract: Radial variations of the amplitude and the energy flux of compressive waves in the solar corona were explored for the first time using a spacecraft radio occultation technique. By applying wavelet analysis to the frequency time series taken at heliocentric distances of 1.5-20.5 RS (solar radii), quasi-periodic density disturbances were detected at almost all distances. The period ranges from 100 to 2000 s. The amplitude of the fractional density fluctuation increases with distance and reaches ~30% around 5 RS , implying that nonlinearity of the wave field is potentially important. We further estimate the wave energy flux on the assumption that the observed periodical fluctuations are manifestations of acoustic waves. The energy flux increases with distance below ~6 RS and seems to saturate above this height, suggesting that the acoustic waves do not propagate from the low corona but are generated in the extended corona, probably through nonlinear dissipation of Alfven waves. The compressive waves should eventually dissipate through shock generation to heat the corona.
48 citations
TL;DR: In this article, the authors compare photospheric line-of-sight magnetograms from the Synoptic Longterm Investigations of the Sun (SOLIS) vector spectromagnetograph (VSM) instrument with observations from the 150-foot Solar Tower at Mt. Wilson (MWO), Helioseismic and Magnetic Imager (HMI) on Solar Dynamics Observatory (SDO), and Michelson Doppler Imager(MDI) on SOHO, and find very good agreement between VSM and the other data sources for both disk-aver
Abstract: We compare photospheric line-of-sight magnetograms from the Synoptic Long-term Investigations of the Sun (SOLIS) vector spectromagnetograph (VSM) instrument with observations from the 150-foot Solar Tower at Mt. Wilson (MWO), Helioseismic and Magnetic Imager (HMI) on Solar Dynamics Observatory (SDO), and Michelson Doppler Imager (MDI) on Solar and Heliospheric Observatory (SOHO). We find very good agreement between VSM and the other data sources for both disk-averaged flux densities and pixel-by-pixel measurements. We show that the VSM mean flux density time series is of consistently high signal-to-noise with no significant zero-offsets. We discuss in detail some of the factors -spatial resolution, flux dependence and position on the solar disk- affecting the determination of scaling between VSM and SOHO/MDI or SDO/HMI magnetograms. The VSM flux densities agree well with spatially smoothed data from MDI and HMI, although the scaling factors show clear dependence on flux density. The factor to convert VSM to HMI increases with increasing flux density (from $\approx$1 to $\approx$1.5). The nonlinearity is smaller for the VSM vs. ~SOHO/MDI scaling factor (from $\approx$1 to $\approx$1.2).
37 citations
Cites methods from "Ground Based Synoptic Instrumentati..."
...A detailed description of the VSM telescope and spectrograph can be found in, e.g., Balasubramaniam and Pevtsov (2011) and Keller, Harvey, and Giampapa (2003)....
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References
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740 citations
TL;DR: In this article, an earth-directed coronal mass ejection (CME) was observed on May 12, 1997 by the SOHO Extreme ultraviolet Imaging Telescope (EIT) and was later observed by the Large Angle Spectrometric Coronagraph (LASCO) as a "halo" CME: a bright expanding ring centered about the occulting disk.
Abstract: An earth-directed coronal mass ejection (CME) was observed on May 12, 1997 by the SOHO Extreme ultraviolet Imaging Telescope (EIT). The CME, originating north of the central solar meridian, was later observed by the Large Angle Spectrometric Coronagraph (LASCO) as a “halo” CME: a bright expanding ring centered about the occulting disk. Beginning at about 04:35 UT, EIT recorded several CME signatures, including dimming regions close to the eruption, post-eruption arcade formation, and a bright wavefront propagating quasi-radially from the source region. Each of these phenomena appear to be associated with the same eruption, and the onset time of these features corresponds with the estimated onset time observed in LASCO. We discuss the correspondence of these features as observed by EIT with the structure of the CME in the LASCO data.
628 citations
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TL;DR: In this article, it is shown that progress in understanding the solar dynamo and explaining the observations can be achieved only through a combination of approaches including local numerical experiments and global mean-field modeling.
Abstract: The solar dynamo continues to pose a challenge to observers and theoreticians. Observations of the solar surface reveal a magnetic field with a complex, hierarchical structure consisting of widely different scales. Systematic features such as the solar cycle, the butterfly diagram, and Hale's polarity laws point to the existence of a deep-rooted large-scale magnetic field. At the other end of the scale are magnetic elements and small-scale mixed-polarity magnetic fields. In order to explain these phenomena, dynamo theory provides all the necessary ingredients including the \(\alpha\) effect, magnetic field amplification by differential rotation, magnetic pumping, turbulent diffusion, magnetic buoyancy, flux storage, stochastic variations and nonlinear dynamics. Due to advances in helioseismology, observations of stellar magnetic fields and computer capabilities, significant progress has been made in our understanding of these and other aspects such as the role of the tachocline, convective plumes and magnetic helicity conservation. However, remaining uncertainties about the nature of the deep-seated toroidal magnetic field and the \(\alpha\) effect, and the forbidding range of length scales of the magnetic field and the flow have thus far prevented the formulation of a coherent model for the solar dynamo. A preliminary evaluation of the various dynamo models that have been proposed seems to favor a buoyancy-driven or distributed scenario. The viewpoint proposed here is that progress in understanding the solar dynamo and explaining the observations can be achieved only through a combination of approaches including local numerical experiments and global mean-field modeling.
516 citations
TL;DR: The GONG project acquires velocity images from a network of six identical instruments distributed around the world and has achieved a duty cycle of 89 percent and reduced the magnitude of spectral artifacts by a factor of 280 in power, compared with single-site observations.
Abstract: Helioseismology requires nearly continuous observations of the oscillations of the solar surface for long periods of time in order to obtain precise measurements of the sun's normal modes of oscillation. The GONG project acquires velocity images from a network of six identical instruments distributed around the world. The GONG network began full operation in October 1995. It has achieved a duty cycle of 89 percent and reduced the magnitude of spectral artifacts by a factor of 280 in power, compared with single-site observations. The instrumental noise is less than the observed solar background.
482 citations
Book•
01 Jan 1986
TL;DR: In this article, the authors describe the Fabry-Perot interferometer and its variants as well as its use, optimisation and applications, and discuss its classical uses in metrology and its contemporary applications.
Abstract: This book describes the Fabry-Perot interferometer and its variants as well as its use, optimisation and applications. The author begins with an historical perspective on the development of the instrument. Because of the quantitative uses of the device, the text tends to be mostly mathematical in its treatment. However, there is also much practical detail on the use and optimization of the Fabry-Perot interferometer and discussion of its classical uses (such as in metrology) and its contemporary applications (such as in lasers). In addition the book contains a comprehensive bibliography summarizing the extensive literature on the subject. This book will appeal both to high-resolution practitioners, such as spectroscopists, and to the laser community, since the Fabrv-Perot is not only an integral part of the laser but is also usea to characterize its optical and spectroscopic behaviour.
307 citations